SEXUAL SELECTION 171 



the hen-birds that are strongest on the wing arrive and mate 

 with the most vigorous cocks, attracted by their trumpet notes, 

 or by whatever other modes of advertisement they may have. 

 Thus the strong pair with the strong, while a male who, through 

 inferior wing power arrives late, has to mate with a weakly 

 belated hen-bird. By this system the young birds of the year 

 will be to some extent divided into two classes, the strong and 

 the weak, and the elimination of the unfit by Natural Selection 

 will be facilitated. But this is not all. Sexual Selection 

 working thus is able to bring about more than the bare 

 superiority to existing conditions which is all that Natural 

 Selection, if it works unaided, can achieve. The migrants 

 under this system can fly more than just well enough to make 

 their two annual journeys. They have a superfluity of wing 

 power, and if any exceptional emergency arises, such as a storm 

 that they have not been able to foresee, then the vigour Sexual 

 Selection has given them may enable them to weather it. Or 

 the environment may become permanently more exacting : the 

 birds of prey may become keener of sight, more unerring in 

 their swoop. Then the strength that Sexual Selection has 

 conferred upon the small bird may stand him in good stead. 



Here I may recall what I said in the previous chapter about 

 the crises that occur in the lives of all animals. 1 Their structure 

 must fit them to stand the severest trials to which they are likely 

 to be subjected, such as severe cold or the attacks of formidable 

 enemies. Such trials will come as occasional crises, and during 

 the intervals they will have a superabundance of vigour. But 

 Sexual Selection may endow them with a vigour even beyond 

 what the most severe crises may demand. It might, in fact, if 

 systematically carried out in a species ennoble every structure and 

 every faculty quite independently of Natural Selection. The 

 individuals thus ennobled would form the aristocracy of the race. 

 This is no doubt what actually to some extent happens, but 

 Natural Selection soon intervenes and makes short work of the 

 common herd. There are more of them than there is room for, or 

 an unusually severe crisis comes, and the aristocracy alone remains. 



1 See pp. 72-77. 



